1. Field of the Invention
The present invention relates to a liquid discharge head for discharging liquid by bubble generation due to the action of heat energy on liquid, a head cartridge using the liquid discharge head, and a liquid discharge device. Further, the present invention relates to a new liquid discharge method including displacement of a movable member and bubble growth, a liquid discharge head, a head cartridge and a liquid discharge device for carrying out this liquid discharge method.
The present invention is an invention which can be applied to devices such as a printer which records on a recording medium, such as paper, thread, fiber, cloth, leather, metal, glass, ceramics and the like, a copy machine, a facsimile including a communication system, and a word processor including a printer section. Further the present invention can be applied to an industrial recording device compositely combined with each type of processing unit. A term xe2x80x9crecordingxe2x80x9d means not only imparting an image having a meaning of a character and a figure or pattern etc., on a recording medium but also imparting an image having no meaning of the pattern etc., thereon.
2. Related Background Art
An ink jet recording process, so called a bubble jet recording process, in which a state change including a rapid volume change of ink (i.e., generation of bubbles) is caused to generate by imparting energy such as heat or the like to the ink, the ink is discharged from a discharge port by an active force due to this state change and the discharged ink is adhered to a medium to be recorded to perform an image formation, has been well known. In the recording device using this bubble jet recording process, as disclosed in publications of the specification of U.S. Pat. No. 4,723,129 and the like, there are generally provided a discharge port for discharging ink, an ink flow path communicated with this discharge port and an electrothermal converting member used as an energy generating means for discharging ink provided in the ink flow path.
According to such recording process, a high quality level image can be recorded at high speed and low noise and a discharge port for discharging ink can be provided at high density in a head in this recording process. Therefore, the recording process has a number of the advantages that a high revolution recording image and such color image could easily be obtained in a compact device. Thus, this bubble jet recording process has recently been used in various office equipment such as a printer, copy machine, facsimile and the like. Further, the recording process is used even in an industrial system such as a printing equipment etc.
With the increased use of the bubble jet technology in products in many fields, the following various demands are recently increased.
For example, an answer to demand of improvement of energy efficiency includes optimization of a heating element in which thickness of a protective film is controlled. This technology has an advantage in that the transmission efficiency of generated heat to liquid is enhanced.
Further, to obtain an extended definition image, there is provided a driving condition for imparting a liquid discharging method in which an improved ink discharge based on a stable bubble generation can be performed. Furthermore, to obtain a liquid discharge head having a high refilling speed of a discharged liquid to a liquid flow path from the viewpoint of the high speed recording, there is also provided a liquid discharge head having improved shapes of the liquid flow path.
A flow path structure and a head producing method disclosed in Japanese Patent Application Laid-Open No. 63-199972, relating to the shapes of the flow path, are patents that take notice of a back wave (pressure in a direction opposite to that toward a discharge port, that is pressure toward a liquid chamber) which is generated with the generation bubbles. This back wave is known as a loss energy since it is not an energy toward the discharge direction.
A head disclosed in the Japanese Patent Application Laid-Open No. 63-199972, has an ink jet head valve which is spaced from a bubbling area of bubbles formed by the heating element and is positioned at the opposite side to the discharge port with respect to the heating element. This valve has an initial position in a manner that it is adhered to the ceiling of the flow path by a head producing method using a plate material, and is hung down in the flow path with the generation of bubbles. This patent is disclosed as a patent in which an energy loss is controlled by controlling a part of the above-mentioned back wave with a valve.
However, in this configuration, as will be found by studying bubble behaviors in a liquid flow path just before and after bubble generation in the flow path supporting liquid to be discharged, suppression of a part of a back wave with a valve is not necessarily useful for discharging liquid. The back wave itself has no direct relation to the discharge of liquid by nature. Therefore, even though a part of the back wave was suppressed, the suppression does not impart a great influence to the discharge of liquid.
The main object of the present invention is to enhance the fundamental discharge properties in a method of discharging liquid by forming bubbles (particularly, bubbles are generated by film boiling) in a liquid flow path, to a level which could not be expected conventionally. The enhancement of the discharge properties was attained by view points which could not be thought.
A part of the present inventors has studied to provide a new liquid drop discharge method using bubbles, which were not obtained, and a head used therein and the like, by reviewing the principles of the liquid droplet discharge. Further the present inventors have made a first technical analysis which starts from the movement of a movable member in a liquid flow path and analyzes the principle of a mechanism of the movable member in the liquid flow path; a second analysis which starts from the principle of the liquid droplet discharge with bubbles; and a third analysis which starts a bubble generation region in a heating element for generating bubbles.
By these first, second and third analyses, quite a new technology for actively controlling the bubbles has been established by allowing the movable member to face the heating element or bubble generation region. Another feature of the present invention is to efficiently displace the bubble growth components on the downstream side to a discharge direction, based on the knowledge of the facts that, taking the energy which bubbles themselves impart to the discharge quantity into consideration, utilization of the bubble growth components on the downstream is a maximum function which can remarkably enhance the discharge properties. Such efficient displacement of the bubbles can lead to enhancements of the liquid discharge efficiency and liquid discharge speed.
The present invention provides a new liquid discharge method and liquid discharge principle which can further improve the above-mentioned epoch-making liquid discharge principle. That is, in the present invention, a principle which can further enhance the liquid discharge efficiency was studied by recognizing the relationship between the displacement of the free end of the movable member and the growth of bubbles obtained from the bubble generation region.
Further, a point that the present inventors have recognized is one that the structure of the liquid flow path greatly contributes to a more efficient use of the above-mentioned liquid discharge principle and to attainment of a higher liquid discharge efficiency and liquid discharge output, so that the liquid flow derived from the bubble growth is efficiently controlled and the displacement of the movable member is efficiently made.
The main object of the present invention is to provide a liquid discharge head, liquid discharge method, head cartridge and liquid discharge device which can further stabilize and enhance the liquid discharge efficiency by aiding the displacement of a movable member over the above-mentioned epock-making liquid discharge principle.
In accordance with one aspect of the present invention, there is provided a liquid discharge head comprising a discharge port for discharging liquid, a liquid flow path provided with a bubble generation means for generating bubbles in liquid and communicated with the discharge port, and a movable member provided facing the bubble generation means in the liquid flow path and having a free end on a downstream side toward the discharge port, a first surface provided with the bubble generation means being continued to at least one second surface of the side wall surface of the liquid flow path and the front end surface having the opening of the discharge port with a curved surface, the first surface being one of surfaces forming the liquid flow path.
In accordance with another aspect of the present invention there is provided a liquid discharge method for discharging liquid by using a liquid discharge head comprising a discharge port for discharging liquid, a liquid flow path provided with a bubble generation means for generating bubbles in liquid and communicated with the discharge port, and a movable member provided facing the bubble generation means in the liquid flow path and having a free end on a downstream side toward the discharge port, a first surface provided with the bubble generation means being continued to at least one second surface of the side wall surface of the liquid flow path and the front end surface having the opening of the discharge port with a curved surface, the first surface being one of surfaces forming the liquid flow path, and displacing the free end of the movable member due to the generation of the bubbles thereby leading the pressure to the discharge port to discharge liquid, wherein when the movable member is displaced due to the generation of the bubbles, liquid is flowed between the movable member and the liquid flow path along the curved surface by the growth of the bubbles.
In the present invention, a first surface provided with the bubble generation means is continued to at least one second surface of the side wall surface of the liquid flow path and the front end surface having the opening of the discharge port with a curved surface, the first surface being one of surfaces forming the liquid flow path. Liquid is flowed between the movable member and liquid flow path along the curved surface by the pressure due to the generation of bubbles. As a result, this liquid flow supports the movable member, and a displacement motion of the movable member and the growth of bubbles are stably made. Accordingly, discharge properties can be enhanced and at the same time the durability of the movable member itself can also be enhanced.
On the other hand, in a contraction process of bubbles, eddy flows are generated around the bubble generation means by the curved face. The eddy flows allow bubbles to separate from the bubble generation means, thereby preventing cavitation impact which is generated upon the disappearance of bubbles, from being directly imparted to the bubble generation means. Thus, the life of the bubble generation means can be enhanced.
In order to effectively generate a flow of the above-mentioned liquid, it is preferable that a width of the liquid flow path is gradually increased in a direction where the displacement of the movable is increased, and that the above-mentioned curved surface is formed so that the concave surface thereof faces a surface provided with the bubble generation means. It is preferable that the curvature of this concave surface is in a range of 2 xcexcm to 20 xcexcm.
The terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d used in this invention are represented as expressions relating to directions in a liquid flow directed from a source of supply for liquid to a bubble discharge port through the bubble generation region (or movable means). Also, the term xe2x80x9cdownstream sidexe2x80x9d relating to bubbles themselves represents a bubble discharge port side section which directly and mainly acts on the discharge of liquid droplets. More particularly, the term xe2x80x9cdownstream sidexe2x80x9d means bubbles which are generated in a region on a downstream side from the center of a bubble relating to the direction of a flow, or on a downstream side from the center of the surface area of the heating element.
Other objects of the present invention will be understood from the following descriptions by those skilled in the art.